Method and apparatus for forward link power control

Abstract

A forward link power control mechanism measures the reverse link power control bits which are transmitted on the forward traffic channel. At the remote station, the reverse link power control bits from multiples base stations or multiple signal paths are measured, combined, and filtered to yield an improved measurement of the forward link signal quality. The reverse link power control bits which are deemed unreliable are omitted from use in the power control loop. The remote station generates a set of forward link power control bit in accordance with the measurements and transmits these bits to all base stations in communication with the remote station. Each base station adjusts its gain of the forward traffic channel in accordance to its measurement of the forward link power control bit. However, the gains of the forward traffic channels of the base stations are corrected periodically so that erroneous reception of the forward link power control bits by the base stations do not accumulate.

We claim:  
     
       1. A method for controlling a forward link transmission power in a CDMA system comprising: 
       measuring amplitude values of a first set of bits received over the forward link, wherein each bit of the first set of bits is transmitted at a transmit power level that is independent of a forward link data rate;  
       comparing said amplitude values against a target energy level; and  
       generating a second set of bits based on said comparing, wherein said second set of bits is used to adjust the forward link transmission power.  
     
     
       2. The method of  claim 1  wherein said target energy level is set at an initial stage of a communication and/or in response to a measured performance of a received signal. 
     
     
       3. The method of  claim 1  further comprising the step of: 
       transmitting said second set of bits to a destination station;  
       wherein said transmission power of said destination station is adjusted in accordance with said second set of bits.  
     
     
       4. The method of  claim 3  wherein each bit of said second set of bits is transmitted after a fixed delay from a latest possible power control bit position of said first set of bits. 
     
     
       5. The method of  claim 3  wherein each bit of said second set of bits is transmitted after a fixed delay from a received bit of said first set of bits. 
     
     
       6. The method of  claim 3  wherein each bit of said second set of bits is transmitted with a pulse having a duration of less than one power control group. 
     
     
       7. The method of  claim 1  further comprising the step of: 
       adjusting said target energy level in response to a measured performance of a received signal.  
     
     
       8. The method of  claim 7  wherein said adjusting step comprises the steps of: 
       increasing said target energy level by an upward step in response to an indication of a frame error; and  
       decreasing said target energy level by a downward step in response to an absence of a frame error.  
     
     
       9. The method of  claim 8  wherein said adjusting step further comprises the step of: 
       maintaining said target energy level if said amplitude values of said first set of bits fall below a minimal energy level.  
     
     
       10. The method of  claim 8  wherein said upward step and said downward step are set at an initial stage of a communication and/or in response to said measured performance of said received signal. 
     
     
       11. The method of  claim 8  wherein said upward step and said downward step are functions of said target energy level. 
     
     
       12. The method of  claim 8  wherein said adjusting step further comprises the step of: 
       maintaining said target energy level in response to an indication of two consecutive frame errors; and  
       wherein said increasing step is in response to an indication of a frame error and an absence of a frame error in two consecutive prior data frames.  
     
     
       13. The method of  claim 1  further comprising the step of: 
       correcting said transmission power in accordance with a set of commands from a system controller.  
     
     
       14. The method of  claim 5  wherein said correcting step comprises the steps of: 
       receiving at least one set of said second set of bits; and  
       selecting a selected set of bits from among said at least one set of said second set of bits;  
       wherein said transmission power is corrected in accordance with said selected set of bits.  
     
     
       15. The method of  claim 1  wherein said measuring step further comprises the steps of: 
       receiving at least one signal path corresponding to said first set of bits;  
       demodulating each of said at least one signal path to obtain a pilot signal and a filtered data;  
       computing a dot product of said pilot signal and said filtered data to obtain a signed scalar output; and  
       combining said signed scalar outputs from said least one signal path to obtain a combined scalar output;  
       wherein said amplitude values of said first set of bits is equal to said combined scalar output.  
     
     
       16. The method of  claim 15  further comprising the step of: 
       filtering said combined scalar output to obtain said amplitude values of said first set of bits.  
     
     
       17. The method of  claim 15  wherein said combining step comprises the steps of: 
       coherently summing said signed scalar outputs from said at least one signal path which carry an identical stream of said first set of bits; and  
       summing said absolute values of said signed scalar outputs from said at least one signal path which carry a non-identical stream of said first set of bits.  
     
     
       18. An apparatus for controlling a forward link transmission power in a CDMA system comprising: 
       a first power control loop for maintaining a quality of a received signal at a target energy level, said first power control loop receiving a first set of bits and a target energy level and providing a second set of bits in response to said first set of bits and said target energy level, wherein each bit of the first set of bits is transmitted at a transmit power level that is independent of a forward link data rate; and  
       a second power control loop for maintaining a measured performance of said received signal, said second power control loop receiving indicators of frame errors and a performance threshold and providing said target energy level to said first power control loop in response to said measured performance and said performance threshold.  
     
     
       19. The apparatus of  claim 18  wherein said first power control loop comprises: 
       receiver means for receiving at least one signal path corresponding to said first set of bits;  
       demodulator means for demodulating each of said at least one signal path to obtain a signed scalar output;  
       combining means for combining said signed scalar outputs from said least one signal path to obtain a combined scalar output; and  
       comparison means for comparing said combined scalar outputs against said target energy level and for producing said second set of bits in response to said comparison.  
     
     
       20. The apparatus of  claim 19  wherein said demodulator means demodulate each of said at least one signal path to obtain a pilot signal and a filtered data, and wherein said demodulator means further comprises: 
       dot product circuit means for producing said signed scalar output based on said pilot signal and said filtered data.  
     
     
       21. The apparatus of  claim 19  wherein said first power control loop further comprises: 
       filter means for filtering said combined scalar output to obtain a filtered output; and  
       wherein said comparison means compares said filtered output against said target energy level.  
     
     
       22. The apparatus of  claim 18  wherein said second power control loop comprises: 
       threshold adjust circuit means for increasing said target energy level by an upward step in response to an indication of a frame error and decreasing said target energy level by a downward step in response to an absence of a frame error.  
     
     
       23. The apparatus of  claim 22  wherein said target energy level is set at an initial stage of a communication and/or in response to a measured performance of said received signal. 
     
     
       24. The apparatus of  claim 22  wherein said upward step and said downward step are set at an initial stage of a communication and/or in response to a measured performance of said received signal.